Field of the Invention
The present invention relates to an RF switch and more particularly an RF switch formed as a monolithically integrated micro electro-mechanical system (MEMS) switch, which includes a rigid beam, a substrate and one or more electrical contacts, monolithically formed with a metal pin pivotally coupled to a substrate, defining a pivot point for the beam forming a teeter-totter that is adapted to be electrostatically actuated to pivot between a contact open position and a contact closed position, which eliminates the flexing of the beam thereby increasing the switch life. 2. Description of the Prior Art
RF switches are generally known in the art. Examples of such switches are described in detail in U.S. Pat. No. 5,578,976, hereby incorporated by reference. Such RF switches are used in various microwave and millimeter applications, such as tunable preselectors, frequency synthesizers as well as automotive applications.
FIG. 1 is illustrative of a known RF micro electro-mechanical system (MEMS) switch. As shown, the MEMS, generally identified with the reference numeral 20, is formed on a substrate 22, with a post 24 formed at one end. A flexible cantilever beam 26 is connected on one end to the post 24. The cantilever beam 26 is adapted to carry an electrical contact 28 on one end that is aligned and adapted to mate with a corresponding contact 29 carried by the substrate 22. An RF input signal is adapted to be connected to the contact 29 which forms an RF input port, while the contact 28 forms an RF output port.
The switch 20 is adapted to be actuated electrostatically. A grounding plate 32 is formed on the substrate 22 while a field plate 34 is formed on the cantilever beam 26. The grounding plate 32 is adapted to be connected to ground while the field plate 34 is adapted to be selectively coupled to a DC voltage source. In operation, in an off state with no voltage applied to the field plate 34, the contact 28 is separated from the contact 29 defining a contact open state, as generally shown in FIG. 1. When an appropriate DC voltage is applied to the field plate 34, the cantilever beam 34 is deflected by the electrostatic forces, causing the electrical contact 28 to mate with the electrical contact 29 allowing the RF input signal to be electrically connected to the RF output port. When the voltage is removed from the field plate 34, the cantilever arm 20 returns to its static position as shown in FIG. 1 due to the restoring forces in the cantilever beam 26.
U.S. Pat. No. 5,552,924 also discloses a micro electro-mechanical (MEM) device formed on a substrate. A post is formed on the substrate for supporting an elongated beam. The elongated beam is center supported and formed with electrical contact on opposing ends. The structure operates electrostatically. More particularly, a DC voltage applied to field plates on the elongated beam result in electrostic forces which cause torsional bending of the beam.
Unfortunately, the configurations discussed above require bending of the cantilever beam everytime the switch operates. Such bending results in reduced switch reliability as well as reduced switch life.
There are other problems associated with such known RF switches, such as relatively high insertion losses, unacceptable in certain applications, such as RF switching applications. More particularly, the cantilever beam, disclosed in U.S. Pat. No. 5,578,976 is formed from silicon dioxide SiO.sub.2 while a composite silicon metal alloy (Al:Ti:Si) is used for the beam in the switch disclosed in U.S. Pat. No. 5,552,994. Unfortunately, the use of such materials for the beam results in a relatively high insertion loss and thus results in reduced sensitivity of the RF switch.
As mentioned above, such RF switches are adapted to be utilized in a wide range of applications, such as frequency synthesizers and the like. Conventional semiconductor RF switches are known to be relatively large and bulky (i.e. 400 in.sup.3 for a 16.times.16 array) making packaging sizes for systems utilizing such RF switches relatively large. As such, micro-machined RF switches have been developed, for example as disclosed in U.S. Pat. Nos. 5,578,976 and 5,552,994. Such micro-machined RF switches have significantly reduced package sizes (i.e. 1 in.sup.3). However, known fabrication techniques for such micro-machined RF switches are incompatible with known HBT and HEMT or CMOS processing techniques, heretofore preventing integration of said RF switches with such HEMT and HBT or CMOS devices.